The invention relates to a procedure for reading the data stored in a transponder which derives its supply energy from an RF interrogation pulse sent to it by an interrogation device and which transmits the data stored in it as an RF response signal modulated by these data. It furthermore relates to a transponder system for the execution of this procedure.
A transponder system is known from the EP 0 681 192 A2 which consists of two units, namely a transponder and an interrogation device. Data are stored in the transponder which may be read by means of the interrogation device. These data may, for example, serve to identify an object within which or to which the transponder is attached. The transmission of the data is in the form of RF signals, which means that reading the data and therefore, to give an example, the identification of the object to which the transponder is attached does not involve any physical contact.
The transponder of the known transponder system is a batteryless transponder which derives its supply energy from an RF interrogation pulse which is sent by the interrogation device. This RF interrogation pulse is rectified in the transponder and used to charge an energy store which in turn provides the supply energy required by the transponder in order to transmit the data stored in it in the form of RF response signals.
Due to this particularity it is obvious that the transmitting power of the transponder is rather low, which means that the range within which the data can still be read correctly by the interrogation device is limited. The greater the distance between the transponder and the interrogation device, the more feeble is the signal received by the retrieval device, so that, of necessity, interference frequencies receivable within the operating area of the transponder system tend to swamp the RF interrogation signal or at least components of this signal and, therefore, make a correct demodulation of the RF interrogation signal impossible.